GB1526085A - Hydraulic pumping arrangements - Google Patents

Abstract

1526085 Controlling variable displacement pumps PLESSEY CO Ltd 26 Oct 1976 [4 Nov 1975] 45724/75 Heading G3P A variable displacement pump 2 for supplying fluid through a valve 82 to a hydraulic system which is normally supplied by a main pump has two piston and cylinder actuators 31, 33 for urging a swash-plate 30 towards maximum and minimum pump displacement positions respectively, and means 70 responsive to a condition in the system (i.e. downstream of the valve 82) for controlling the supply of liquid from the system to operate means 50 through which liquid is supplied to the actuator 33, the means 50 being operative, when it is receiving liquid, to move the swash-plate to an on-swash condition to supply liquid to the system in the event of a lack of output from the main pump. When the pump is started, non-return valve 82 is closed and no liquid is pumped to the valve 70, and the spool of valve 50 is urged to the right (as shown in Fig. 1) by spring 100; thus liquid supplied to the actuator 31 moves the swash-plate 30 to the maximum displacement position, and none reaches the actuator 33 until the pressure acting on the valve spool balances the spring. As the pressure rises the valve 82 is opened and fluid is supplied through the valve 70 to act on the spool of valve 50 in opposition to the pump pressure, so that this valve (and hence the pump displacement) is controlled in dependence on the pressure drop across orifice 80. When the pressure in the system reaches a predetermined level the valve 70 interrupts the supply of control liquid to the valve 50, which cuts off the supply to the actuator 33, so that the swash-plate is moved to the minimum displacement position, and the pump remains in this stand-by condition until the pressure in the system falls to allow the valve 70 to open. The valves 50, 70 are described in detail with respect to Figs. 2-4 (not shown).